One of the issues with variable capacitor materials, dielectrics—whose dielectric permittivities change when a electric bias is applied, is that these materials must be crystalline. These materials have a perovskite structure. Many of these tunable materials have higher losses than are desired, which lowers the performance of the functional devices.
In addition, these materials have large temperature coefficients of capacitance. Therefore, it is hard to keep a constant capacitance without also knowing the temperature of the system. Monitoring and feedback loops are commonly required to compensate for changes in capacitance with temperature. Therefore, decreasing the effective overall change in capacitance can eliminate the need for a compensating circuit.
Further, these materials experience upper limits in response to frequency somewhere in the 15–45 GHz range. Depending on the material, responsiveness of the material decreases at higher frequencies.
The crystalline nature of these materials depends on deposition parameters (temperature, etc.) and substrate properties. It is important that the crystalline nature of the material is optimized to increase performance. Also, boundaries can lead to loss and leakage in the capacitance structures or RF signal and lower the amount of material that experiences the dielectric change.
The scope of the current invention enables materials to be formed that have a significantly reduced temperature coefficient of capacitance and can be put on a wide range of substrates using a wide range of processes. The invention is keyed around a composite of materials or a structure of materials where a wide range of conductive and non-conductive materials can be formed in a variety of ways to yield the desired functional capacitors. By using materials with both negative and positive temperature coefficients of capacitance, it is envisioned that an overall temperature coefficient of capacitance approaching zero can be achieved. These materials could also have utilization in the area of optics.
Composite materials formed of dielectric material containing embedded particulates of conducting material have been shown to have high dielectric values.
It has been shown in the past that by forming a nano-laminate of silica and platinum, a higher value of capacitance can be achieved with respect to pure silica. The enhanced capacitance is due to the formation of dipoles within the thin platinum layers. The free electrons from the platinum are able to act as dipoles between the electrodes; thus, adding to the capacitance of the structure. In a similar way, by having nano-laminates and/or nano-clusters or particulates of a conductive material in a matrix of an insulator material, the capacitor can be enhanced. This is achieved by the additional charge separation possible in the isolated conductive layers or particulates, which enables a higher capacitance on the electrodes on either side of the material.